Optimizing nutrient removal of moving bed biofilm reactor process using response surface methodology

[Display omitted] •A 3-stages treatment achieved high organics (≥95.5%)and nutrients (≥92.5%) removals.•Surface response methodology identified optimum operational conditions.•Attached biofilm nitrifying activity was 4 times higher than activated sludge system.•Maximum nitrogen and phosphorous removal efficiencies were 92.54%, 94.70%.•Optimum removals were achieved at 2 h-hydraulic retention time and 1.5 recycle ratio. The potential of 3-stages process (anaerobic, anoxic and moving bed biofilm reactor (MBBR)) for organic matter and nutrient removals from secondary WWTP effluents at various hydraulic retention time (HRT) and nitrate recycle ratio (R) was investigated. Percentage removals of total nitrogen (%TNremoval) and phosphorous (%TPremoval) were optimized using response surface methodology (RSM). Under optimized conditions (HRTtotal = 12.8 hr and R = 1.5) significant chemical oxygen demand removal (%CODremoval), %TNremoval and %TPremoval of 95.5%, 96.2%, 94.70% were attained. The MMBR effectively reduced organic matter and nutrient under low HRT and R. %TNremoval was improved by increasing the HRTR2 up to 1.5 h at R ≤ 2. Bio-uptake of phosphorus and nitrate is controlled by release of secondary phosphorous. Reactors demonstrated stable biofilm characteristics except for a slight decrease in biofilm thickness due to flow-shear stress. The 3-stages process performed four times higher than suspended growth process and similar to 5-stage Bardenpho-MBBR.